This invention relates generally to position detection systems and more particularly systems for detecting the position of cable or other elongated continuous flexible materials which are buried in the ground by positionable means carried by a vehicle traversing the ground.
It is common practice to lay telephone or other communications cable along the right of way of a railroad. One particularly effective means for accomplishing that task is a railroad cable laying apparatus like that shown and claimed in U.S. Pat. No. 3,546,887 (Helmus), invented by one of the co-inventors of the subject invention, assigned to the same assignee as this application and whose disclosure is incorporated by reference herein.
The railroad cable laying apparatus disclosed in that patent basically comprises a railroad car adapted to be moved along the track. The car supports a rearwardly trailed elongated arm which can extend laterally from a position on the car to any position to the side thereof so as to draw a blade element through the ground to form a kerf within which continuous flexible material, such as a signal or electrical cable, is deposited by a cable chute also carried by the blade. The arm is an articulated member including plural jointed sections and is positionable by hydraulic components to adjustably locate the blade depositing the cable at selected depths and distances from the railroad track. Release means including a relief valve, check valve and associated hydraulic cylinder are provided to prevent damage to the blade in the event it impacts an object (buried or otherwise) in its path.
After a cable has been laid, whether by the apparatus of the aforementioned patent, or by some other apparatus, it is frequently necessary to service the cable, such as if a breakage occurs. In order to effectuate cable servicing, it is a common practice to provide what are known as "as built" drawings showing the position of the cable as buried. Heretofore, the drawings have been generated by data manually accumulated during the cable laying process. For example, it is a common practice to provide markers adjacent the track at pre-selected intervals. As the rail car bearing the blade/cable chute passes each marker, the position of the plow with respect to the car and to the ground is measured, manually, e.g., by the insertion of a yardstick or other measuring device into the kerf to determine the depth of the cable while also measuring the distance from the car to the kerf. The data is then recorded either by writing it down or by dictating the readings orally onto magnetic tape.
As will be appreciated, the foregoing means for collecting the data so that an "as built" drawing can be made is not very precise, is labor intensive, is relatively expensive and is not conducive to automated drawing generation.